w140 Wiring Harness Replacement -- Easy? 1994 S420
 

All,

I've been told I need to replace my 1994 S420 wiring harness. The MB dealer wants $1500 to do it, but I'd rather pay Phil $450 for the part. Would this be a hard replacement?

Thanks!

Don

Not difficult for a experienced DIYer! Should take 3-4 hrs, start by laying the new harness out & seeing just what you need to disconnect.

Thanks MB Doc! Is the harness "plug and play" i.e. just mostly connectors, or are there screw terminals and soldering to mess with? Will i have to route wires inside the car, and how much dissasembly and wire routing is involved?

All underhood, the harness passes thru the bulkhead just behind the engine & connects on the right inner apron.. The connectors just "plug-in".

Are the replacement wiring harnesses going to corrode like the old ones do, or did they fix the problem with the replacement harnesses?

Regards,
Bryan

Wire Harness Replacement
 

I bought an OEM Mercedes main engine wire harness from Phil for my 1995 E420, because the dealer wanted way too much.

I did just as Phil advised...lay the new harness in place over where the old wires go. I then started at the main connection and worked my way out to the injector wires and beyond. The only issue was that a few wires at the very end of the harness could clip into place two or more ways. I couldn't believe that Mercedes would not put a notch or other feature in the connector, so that you could only put it on one way. For these instances, be sure to look at the wire color coding (stripe) or how the old connector is positioned. Only one was not obvious. The engine-mounted device had 4 equally spaced pins (forming a square) that a connector fit onto. You could have rotated the connector 90 degress and plugged it in four different ways (only one correct, I assume). When I pulled the old connector off, I looked and the connector holes were numbered. I made sure that the new connector had the same numbered holes aligning in the same manner before inserting it onto the pins.

Car runs like a champ now and I love to have saved around $1,000.

Thanks for the awesome reply korgermeister!

The bad wiring harnesses were installed in ALL Mercedes models coming out in 1992 - 1994 or something, right?

I have a W140 1993 300SE, and I worry that I ave a deteriorating harness. I have read that the '94 C-Class takes about 24 hours by Mercedes to replace (big BIG $$$$$) but I read here that people are replacing their harnesses by themselves! :eek:

I sure hope this is possible for a DIY person.

By the way, is your new harness made out of non-deteriorating material?

Regards,
Bryan

Is this at all similar to the wiring harness in a 1995 S600?

New Wire Harness
 

What I heard is that Mercedes experimented with a different type of wire insulation (plastic) back then that was more environmentally friendly...would decompose easily when the car was eventually scrapped. There was a problem with the plastic getting brittle and breaking up much sooner than they anticipated. Larger Mercedes engines put out quite a bit of heat.

I would assume that 9 model years later (in the case of my car), they would be making more durable harnesses, but don't know for sure.

Bosch North America said that the bad wire harness and a known software error in the LS-SFI unit are known problems at Bosch for many '94/'95 models. Would probably have been recall issues on American cars.

To answer pcmaher, I would assume that a 1995 S600 would have a similar wire harness that a DIY could do without too much trouble. Not sure though, as I am not familiar with the 600 engine, but just a larger engine and more cylinders. My job took me 3-4 hours.

Any one replaced the wiring harness as a DIY project on a '95 E300D? How long did it take, and how difficult is it to do on this model car?

How much was the harness?

Thanks

Phil

How can dealer justify the charge?
 

ddrake3: "I've been told I need to replace my 1994 S420 wiring harness. The MB dealer wants $1500 to do it, but I'd rather pay Phil $450 for the part."

M.B.DOC: "Not difficult for a experienced DIYer! Should take 3-4 hrs"

ddrake3: "Is the harness plug and play i.e. just mostly connectors, or are there screw terminals and soldering to mess with? Will i have to route wires inside the car, and how much dissasembly and wire routing is involved?"

M.B.DOC: "All underhood, the harness passes thru the bulkhead just behind the engine & connects on the right inner apron.. The connectors just "plug-in."

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I may have misunderstood this, but apparently MB dealer wants $1000 labor to basically unplugging old wires replacing with new; all underhood, without special tools, etc. So 8-10 hours labor charge for a seemingly simple 3-4 DIY job?

I don't think you've misunderstood but the difference is not all labor. At the dealership you are dealing with two profit centers - parts and service. The dealer parts price is sometimes 2 or 3 times what it is elsewhere. Labor rates are high and while they have a hard time fudging the labor hours they will almost always be on the high side there as well. They don't have to justify their prices - they're the dealer - they have a lot of customers who don't ask.

The wiring harness labor operations are misleading at first glance.

104's are a solid 3-4 hr DIY job.
119's a little more.
1994-95 C220 is a real bear, very close quarters. Buried under the intake.
Don't undertake that task if you are in a time crunch.
It WILL take longer than you expect.

The V-12's are a piece of cake.
Lays right on top.

Note--the M119s often have a suspect second,deteriorating harness for the
alternator/starter/oil level sensor. Less expensive, and easier to change,
but worth a look while inspecting the injector harness.

We always check them both, and the second harness is needed approx 1/2 the time.

We have seen no repeat failures of harnesses, but only time will tell.

Thanks for this. I now own a 94 E420 and planning on changing the harness, what would the part number be for the alernator/starter/oil level harness and can it be replaced without pulling engine parts out ? thanks :)

i'm in the same boat on my 93 with the secondary, or lower wiring harness. would be interested in any details as well.